FIGS. 7(A) and 7(B) show conventional brush devices for a small-sized motor, wherein FIG. 7(A) is a view showing, on an enlarged scale, one of the paired brush devices, and FIG. 7(B) is a view of a casing cover of the small-sized motor to which the brush devices are attached, as viewed from the interior of the motor (see Patent Document 1). The illustrated brush device is composed of a carbon brush to come into sliding contact with a commutator, a brush arm which holds the carbon brush pressed fitted thereinto, and a brush base coupled to the brush arm by means of staking. A central portion of the brush base is cut and raised so as to form a receptacle terminal. Therefore, a hole corresponding to the raised receptacle terminal is formed in the central portion of the brush base.
The conventional brush devices are press-fitted into the casing cover and held thereby. The casing cover has external terminal insertion openings into which external terminals are inserted for external electrical connection. Paired magnets (not shown) are disposed in the motor casing to be located on opposite sides with respect to the left-right direction of FIG. 7(B). The two brush arms extend approximately perpendicularly to a line connecting the centers of the magnets, from one of flat portions of the motor casing located on upper and lower sides, respectively, in FIG. 7(B). By virtue of such a configuration, despite the receptacle terminal having a sufficiently large length, a portion of the receptacle terminal which comes into contact with an external terminal can be provided at a position near the corresponding external terminal insertion opening. Therefore, the brush device can be applied in the case where the length of the external terminal is short.
However, because of an internal terminal structure using the receptacle terminal, the brush arm length, which is the distance from the brush arm fixed end to the brush position, cannot be increased. When the brushes wear, the brush arms turn about their fixed ends toward the commutator. In the case where the brush arm length is short, the turn angles of the brush arms become large when the brushes wear, raising a problem in that a phase shift (a deviation of a circumferential position at which electricity is supplied to the commutator, from an initial neutral position of each brush at which the brush initially comes into contact with the commutator) becomes large. Further, since the brush arm length is short, the brush arms deform when the brushes are opened during assembly of the motor (the brush arms are apt to cause permanent set). In addition, since the pressure under which the carbon brushes come into contact with the commutator changes more greatly when the carbon brushes wear, stable contact between the brushes and the commutator cannot be attained. Further, when external terminals are inserted, their tip end portions come into contact with the corresponding receptacle terminals in a sliding-up direction (a direction opposite the direction in which the receptacle terminals extend from the corresponding brush bases), and as a result the receptacle terminals may deform.
FIG. 8 is a view of conventional brush devices in which two carbon brushes are disposed such that a line connecting the carbon brushes inclines in relation to a horizontal center line (a magnet center line) (see Patent Document 2). Two brush arms extend approximately parallel to the flat portions of the motor casing. Although the carbon brushes are arranged along the inclined line, there is a limit to the extent to which the lengths of the brush arms can be increased, because the brush arms are approximately parallel to the flat portions. Further, in the case of the illustrated brush apparatus, when external terminals are inserted, their tip end portions may come into contact with the brush arms. Further, when the external terminals are inserted, their tip end portions come into contact with the corresponding receptacle terminals in the sliding-up direction, and as a result the receptacle terminals may deform.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2001-136712
Patent Document 2: Japanese Utility Model Application Laid-Open (kokai) No. H4-80255